Semiconductor light emitting device having a semiconductor layer formed by selective growth

ABSTRACT

Semiconductor light emitting devices are provided. The semiconductor light emitting device includes a base body, a selection mask having a stripe-shaped opening portion, the selection mask being formed on the base body, a semiconductor layer formed by selective growth from the opening portion in such a manner as to have a ridge line substantially parallel to long-sides of the opening portion, and a first conductive type cladding layer, an active layer, and a second conductive type cladding layer, which are formed on the semiconductor layer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/091,954 filed on Mar. 5, 2002 now U.S. Pat. No. 6,881,982,the disclosure of which is herein incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to semiconductor light emitting devicesand processes for producing same. More particularly, the presentinvention relates to a semiconductor light emitting device, a displayunit, a method of fabricating a semiconductor light emitting device, anda method of fabricating a semiconductor laser having wurtzite typecompound semiconductor layers such as GaN based semiconductor layersthat are formed by selective growth.

Conventionally, when manufacturing a semiconductor light emittingdevice, a semiconductor laser device or a light emitting diode isfabricated by forming a selection mask on a sapphire substrate andselectively growing a semiconductor layer made from a nitride such asgallium nitride through an opening in the selection mask. Sapphire isoften used as a substrate for growing gallium nitride. However,dislocations often occur in the crystals, at a high density, due tomismatches between the crystal lattices of the sapphire substrate andgallium nitride. The following methods are known to reduce crystaldefects: a method of forming a low temperature buffer layer on asubstrate; a method of combining usual crystal growth with selectivecrystal growth in the lateral direction (ELO: Epitaxial LateralOvergrowth as described in Japanese Patent Laid-open No. Hei 10-312971);and a method of forming a gallium nitride based semiconductor laser, inwhich stacked layers having tilt planes are formed by selective growth(see Japanese Patent Laid-open No. Hei 11-312840).

Conventionally, an image display unit is configured by arranging pixelsin a matrix. Each pixel is composed of a combination of light emittingdiodes or semiconductor lasers of blue, green and red. An image isdisplayed by independently driving the respective pixels. The imagedisplay unit can be also used as a white light emitting unit or anillumination unit by allowing the light emitting devices of blue, green,and red to simultaneously emit light of blue, green, and red. Inparticular, since a light emitting device using a nitride basedsemiconductor has a band gap energy ranging from about 1.9 eV to about6.2 eV, a number of light emitting devices capable of emitting light ofmany colors can be fabricated using only semiconductor layers made fromone kind of material (i.e., the nitride based semiconductor), therebyeasily realizing a full-color display. Multi-color light emittingdevices using nitride based semiconductors have been studiedextensively. It is to be noted that the term “nitride” used hereindescribes a compound which contains one or more of B, Al, Ga, In, and Taas group III elements and N as a group V element, and which may containimpurities in an amount of about 1% or less of the total amount or about1×10²⁰ cm³ or less.

In the above-described method, which makes use of selective crystalgrowth in the lateral direction for reducing through-dislocations from asubstrate, and in the crystal growth method, in which a facet structureis formed in a growth region for reducing through-dislocations from asubstrate, it is possible to bend through-dislocations from a substratein the lateral direction by the facet structure portion or the like, andhence to significantly reduce crystal defects. However, to form a lightemission region including an active layer after selective crystal growthin the lateral direction or formation of the facet structure, theselective crystal growth in the lateral direction must be furthercontinued or the facet structure is buried in order to obtain a flatplane on which the light emission region is to be formed. As a result,the number of processing steps is increased and the time required forfabricating the device is prolonged.

The above-described gallium nitride based semiconductor laser and itsfabrication method are disclosed in Japanese Patent Laid-open No. Hei11-312840. When manufacturing a device according to this method, aconductive selection mask is formed in an approximately center portionof an opening portion of an insulating selection mask, to obtain astacked structure having a triangular shape in cross-section formed byselective growth. In such a semiconductor laser, however, the stackedstructure having the triangular shape in cross-section is only used as ahigh resistance region for concentrating a current at an active layerlocated at the center portion. Therefore, even though a (1-101) plane(which is called an S-plane) appearing on a tilt or a slant plane isexcellent for repeatability of fabrication, a region as the active layeris limited to the vicinity of the conductive selection mask at thecentral portion held by the stacked structure having the triangularshape in cross-section. Accordingly, it is difficult to control a filmquality of the active layer. As a result, the repeatability of thefabrication of the whole device is degraded.

SUMMARY OF THE INVENTION

An object of the present invention is, therefore, to provide asemiconductor light emitting device, a display unit, a method offabricating a semiconductor light emitting device, and a method offabricating a semiconductor laser, which reduce crystal defects, such asthrough-dislocations, without increasing the number of fabrication stepsand enhance repeatability of fabrication.

According to an embodiment of the present invention, a semiconductorlight emitting device is provided. The device includes a base body and aselection mask formed on the base body. The selection mask defines astripe-shaped opening portion having long-sides. A semiconductor layeris formed by selective growth from the opening portion such to have aridge line substantially parallel to the long-sides of the openingportion. Further, a first conductive type cladding layer, an activelayer, and a second conductive type cladding layer, are formed on thesemiconductor layer.

According to the above-described semiconductor light emitting device,the selection mask having the stripe-shaped opening portion is formedand the semiconductor layer having a ridge line is formed by selectivegrowth from the opening portion. As a result, tilted crystal planesextending from the ridge line to the selection mask are formed, and thefirst conductive type cladding layer, the active layer, and the secondconductive type cladding layer are formed on the semiconductor layerhaving the tilted crystal planes, to obtain a light emitting structure.In the semiconductor layer having the ridge line, crystallinity isrelatively stable in the direction extending along the ridge line, andit is possible to suppress a variation in characteristics of the lightemitting device. Since an electrode is formed on the second conductivetype cladding layer, with its position limited to a region havingdesirable crystallinity, it is possible to suppress a variation betweenone and another of the devices.

According to another embodiment of the present invention, asemiconductor light emitting device is provided. The device includes abase body and a selection mask formed on the base body. The selectionmask defines a stripe-shaped opening portion extending with itslongitudinal direction taken as a (1-100) direction or a (11-20)direction or a direction tilted from a (1-100) direction or a (11-20)direction by an angle ranging from about 0.2° to about 20°. Asemiconductor layer is formed by selective growth from the openingportion such as to have a ridge line substantially parallel to thelongitudinal direction of the opening portion. A first conductive typecladding layer, an active layer, and a second conductive type claddinglayer, are formed on the semiconductor layer.

According to the above-described semiconductor light emitting device,since the longitudinal direction of the stripe-shaped opening portion ofthe selective growth mask is taken as the (11-20) direction or the(1-100) direction, it is possible to easily form the semiconductor layerhaving the ridge line substantially parallel to the longitudinaldirection of the opening portion. Also, since the longitudinal directionof the stripe-shaped opening portion of the selective growth mask isalternatively taken as the direction tilted from the (11-20) directionor the (1-100) direction by an angle ranging from about 0.2° to about20°, it is possible to easily form the semiconductor layer having theridge line substantially parallel to the longitudinal direction of theopening portion. In the latter case, that is, in the case where thelongitudinal direction of the opening portion is tilted from the (11-20)direction or the (1-100) direction by a specific angle, crystal stepstend to be made regular in the whole of a crystal plane. Accordingly, itis possible to significantly reduce a variation between one and anotherof the devices by forming an electrode in the region in which theregular crystal steps are formed.

In further embodiments of the present invention, a display unit can befabricated by arranging a number of semiconductor light emitting devicesdescribed in each of the previous embodiments of the present invention,and a semiconductor laser device can be fabricated by forming resonanceplanes onto the display unit by cleavage or the like.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1A is a plan view of a semiconductor light emitting deviceaccording to a first embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend in a(1-100) direction or a (11-20) direction, and FIG. 1B is a sectionalview taken on line b—b of FIG. 1A.

FIG. 2 is a side view of a portion of the semiconductor light emittingdevice according to the first embodiment, showing one of the tilt planesof the semiconductor layers and an electrode formed thereon.

FIG. 3A is a plan view of a semiconductor light emitting deviceaccording to a second embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend with itslongitudinal direction tilted from the (1-100) direction or the (11-20)direction by a slight angle, and FIG. 3B is a sectional view taken online b—b of FIG. 3A.

FIG. 4 is a side view of a portion of the semiconductor light emittingdevice according to the second embodiment, showing one of the tiltplanes of the semiconductor layers and an electrode formed thereon.

FIG. 5A is a plan view of a semiconductor light emitting deviceaccording to a third embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend in the(1-100) direction or the (11-20) direction, and FIG. 5B is a sectionalview taken on line b—b of FIG. 5A.

FIG. 6 is a side view of a portion of the semiconductor light emittingdevice according to the third embodiment, showing one of the tilt planesof the semiconductor layers and an electrode formed thereon.

FIG. 7A is a plan view of a semiconductor light emitting deviceaccording to a fourth embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend with itslongitudinal direction tilted from the (1-100) direction or the (11-20)direction by a slight angle, and FIG. 7B is a sectional view taken online b—b of FIG. 7A.

FIG. 8 is a side view of a portion of the semiconductor light emittingdevice according to the fourth embodiment, showing one of the tiltplanes of the semiconductor layers and an electrode formed thereon.

FIG. 9 is a side view of a portion of the semiconductor light emittingdevice according to a fifth embodiment, showing one of the tilt planesof the semiconductor layers and an electrode formed thereon.

FIG. 10A is a plan view of a semiconductor light emitting deviceaccording to a sixth embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend in a(1-100) direction or a (11-20) direction, and FIG. 10B is a sectionalview taken on line b—b of FIG. 10A.

FIG. 11 is a side view of a portion of the semiconductor light emittingdevice according to the sixth embodiment, showing one of the tilt planesof the semiconductor layers and an electrode formed thereon.

FIG. 12A is a plan view of a semiconductor light emitting deviceaccording to a seventh embodiment of the present invention, showing astate of the device before and after selective growth from an opening ofa selection mask which is formed in such a manner as to extend with itslongitudinal direction tilted from the (1-100) direction or the (11-20)direction by a slight angle, and FIG. 12B is a sectional view taken online b—b of FIG. 12A.

FIG. 13 is a side view of a portion of the semiconductor light emittingdevice according to the seventh embodiment, showing one of the tiltplanes of the semiconductor layers and an electrode formed thereon.

FIG. 14 is a side view of a portion of the semiconductor light emittingdevice according to an eighth embodiment, showing one of the tilt planesof the semiconductor layers and an electrode formed thereon.

FIG. 15 is a sectional view showing a portion of a semiconductor lightemitting device according to a ninth embodiment of the presentinvention.

FIGS. 16A and 16B are views illustrating steps of fabricating asemiconductor laser device according to a tenth embodiment of thepresent invention, wherein FIG. 16A is a plan view showing a devicestate after formation of electrodes, and FIG. 16B is a sectional viewtaken on line b—b of FIG. 16A.

FIG. 17 is a sectional view showing a portion of the semiconductor laserdevice shown in FIGS. 16A and 16B, illustrating the method offabricating a semiconductor laser device according to the tenthembodiment.

FIGS. 18A and 18B are views illustrating steps of fabricating asemiconductor laser device according to the tenth embodiment, whereinFIG. 18A is a plan view showing a device state after cleavage, and FIG.18B is a sectional view taken on line b—b of FIG. 18A.

FIG. 19 is a sectional view showing a portion of the semiconductor laserdevice shown in FIGS. 18A and 18B, illustrating the method offabricating a semiconductor laser device according to the tenthembodiment.

FIG. 20 is a partial plan view of a display unit according to aneleventh embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A semiconductor light emitting device according to an embodiment of thepresent invention is manufactured by forming a selection mask having astripe-shaped opening portion on a base body, forming a semiconductorlayer having a ridge line parallel to long-sides of the stripe-shapedopening portion by selective growth from the opening portion of theselection mask, and stacking a first conductive type cladding layer, anactive layer, and a second conductive layer on the semiconductor layer.

The base body used for a semiconductor light emitting device accordingto an embodiment of the present invention is not particularly limitedinsofar as a wurtzite type compound semiconductor layer can be formedthereon. For example, a substrate made from sapphire (Al₂O₃, whosedesirable crystal plane is an A-plane, R-plane, or C-plane), SiC (havinga structure of 6H, 4H or 3C), GaN, Si, ZnS, ZnO, AlN, LiMgO, LiGaO₂,GaAs, MgAl₂O₄, or InAlGaN can be used as the base body. Preferably, thematerial used for forming the base body has a hexagonal or cubic system,and more preferably, has the hexagonal system. When using a sapphiresubstrate, preferably a sapphire substrate with the C-plane of sapphiretaken as a principal plane thereof, which has been often used forgrowing a gallium nitride (GaN) based compound semiconductor thereon, isused. It is to be noted that the C-plane of sapphire taken as theprincipal plane of the substrate in the present invention may be tiltedfrom the strict C-plane by an angle ranging from about 5° to about 6°. Asilicon substrate, which has been widely used for fabricatingsemiconductor devices, may be also used as the base body.

It is noted that the plane terminology (e.g., S-plane, C-plane or thelike) as used herein denotes crystal planes in accordance with Millerindices of a hexagonal crystal system. Where appropriate, throughout thespecification, these planes are intended to include more than one planein the hexagonal crystal system. For example, the S-plane is listedabove as corresponding to the (1-101) plane, but it should be understoodthat, where appropriate, the S-plane is intended to include one or moreof the planes relating to the family of planes making up a crystalstructure having the S-plane. For example, if the crystal structurebeing described is a hexagonal pyramid having the S-plane, planescorresponding to each side face of the hexagonal pyramid would beincluded in the family of planes denoted by the S-plane. For example, inaddition to the (1-101) plane, a hexagonal pyramid has side facescorresponding to the (10-11), (01-11), (−1101) and (0-111) planes.

The base body, used as an under layer on which a selection mask forselective growth is to be formed, may be the above-described substrateitself. However, to obtain good crystallinity at the time of selectivegrowth, the base body according to an embodiment of the presentinvention may be of a two-layer structure having the substrate and anunder growth layer such as a buffer layer formed on the base body. Theunder growth layer may be a compound semiconductor layer, which ispreferably made from a compound semiconductor having a wurtzite typecrystal structure such that a facet structure will be formed thereon inthe subsequent step. Specifically, the compound semiconductor layer maybe made from a nitride semiconductor having a wurtzite type crystalstructure, a BeMgZnCdS based semiconductor, a BeMgZnCdO based compoundsemiconductor, or the like. As the nitride semiconductor having awurtzite type crystal structure, there may be used a group III basedcompound semiconductor, for example, a gallium nitride (GaN) basedcompound semiconductor, an aluminum nitride (AlN) based compoundsemiconductor, an indium nitride (InN) based compound semiconductor, anindium gallium nitride (InGaN) based compound semiconductor, an aluminumgallium nitride (AlGaN) based compound semiconductor, or the like.Preferably, a gallium nitride based compound semiconductor is used. Inan embodiment, an undoped GaN layer may be formed on a sapphiresubstrate and a Si-doped GaN layer may be formed thereon. It is to benoted that, in an embodiment of the present invention, InGaN, AlGaN, GaNor the like does not necessarily mean a nitride semiconductor havingonly a ternary or binary mixed crystal structure. For example, InGaN cancontain an impurity such as a trace of Al in a range not changing thefunction of InGaN without departing from the scope of the presentinvention. In this specification, the term “nitnue” describes a compoundwhich contains one or more of B, Al, Ga, In, and Ta as the group IIIelements and N as the group V element, and which may contain impuritiesin an amount of about 1% of the total amount or less, or about 1×10²⁰cm³ or less.

In an embodiment, the above-described compound semiconductor layer maybe grown by one of various vapor phase growth processes, for example, ametal organic chemical vapor deposition (MOCVD) (including a metalorganic vapor phase epitaxial (MOVPE) growth process), a molecular beamepitaxial growth (MBE) process, a hydride vapor phase epitaxial growth(HVPE) process, and the like. The MOVPE process is advantageous ingrowing the compound semiconductor layer with good crystallinity at ahigh processing rate. In the MOVPE process, alkyl metal compounds aretypically used as Ga, Al and In sources. Preferably, TMG (trimethylgallium) or TEG (triethyl gallium) is used as the Ga source, TMA(trimethyl aluminum) or TEA (triethyl aluminum) is used as the Alsource, and TMI (trimethyl indium) or TEI (triethyl indium) is used asthe In source. Further, in the MOVPE process, a gas such as ammonia,hydradine, or the like may be used as a nitrogen source while silane gasor the like may be used as an Si (impurity) source. Also, germane gas orthe like may be used as a Ge (impurity) source, Cp2Mg (cyclopentadienylmagnesium) or the like may be used as a Mg (impurity) source, and a DEZ(diethyl zinc) gas or the like may be used as a Zn (impurity) source.According to the MOVPE process, for example, an InAlGaN based compoundsemiconductor layer can be formed on a substrate by epitaxial growth bysupplying the above gases to a front surface of the substrate heated,for example, at 600° C. or more, to decompose the gases.

According to an embodiment of the semiconductor light emitting device ofthe present invention, a selection mask having a stripe-shaped openingportion is formed on a surface of the above-described compoundsemiconductor layer taken as the under growth layer for crystal growth,and a semiconductor layer having a ridge line parallel to long-sides ofthe stripe-shaped opening portion of the selection mask is formed byselective growth from the opening portion of the selection mask.

In an embodiment, the mask is a growth obstruction layer, which isformed on a buffer layer as the under growth layer or another layerformed on the substrate (or may be directly formed on the principalplane of the substrate). Preferably, the mask is formed of an insulatingfilm such as a silicon oxide film or a silicon nitride film. The mask isformed into a stripe-shape. A shape of each of end portions onshort-sides of the mask may be a linear shape, a circular-arc shape, ora polygonal shape such as a triangular, pentagonal, or hexagonal shape.

After formation of the mask for selective growth, a semiconductor layerhaving a ridge line parallel to long-sides of the stripe-shaped openingportion of the mask is formed by selective growth from the stripe-shapedopening portion of the mask. The crystal growth may be performed inaccordance with the same manner as that for forming the above-describedcompound semiconductor layer. For example, one of the various vaporphase growth processes (e.g., MOCVD, MOVPE, MBE, HVPE, or the like) maybe used.

According to an embodiment of the semiconductor light emitting device ofthe present invention, a semiconductor layer having a ridge lineparallel to long-sides of the opening portion of the mask is formed byselective growth from the opening portion of the mask. Each of a pair ofcrystal planes of the semiconductor layer, which are located on bothsides of the ridge line, is preferably selected from a (1-101) plane(which is called an S-plane), a (11-22) plane, and planes substantiallyequivalent thereto. A plane substantially equivalent to the S-plane orthe (11-22) plane includes a plane tilted from the S-plane or the(11-22) plane by an angle ranging from about 5° to about 6°. The pair ofcrystal planes are planes tilted downwardly from the ridge line. Forexample, if the C⁺-plane is taken as the substrate principal plane, itis possible to easily form the S-plane or a plane equivalent thereto, orthe (11-22) plane or a plane substantially equivalent thereto. Whenperforming selective growth, the S-plane or the (11-22) plane as thetilt plane tilted from the principal plane of the base body is a stableplane which is relatively easily, selectively grown on the C⁺-plane. TheC⁺-plane and C⁻-plane are present as the C-plane, and similarly, theS⁺-plane and S⁻-plane are present as the S-plane. In this specification,unless otherwise specified, the S⁺-plane, which is grown on the C⁺-planeof a GaN layer, is taken as the S-plane. The S⁺-plane is more stablethan the S⁻-plane. It is to be noted that the C⁺-plane is expressed by a(0001) plane in Miller indices of a hexagonal crystal system.

When forming a crystal layer by growing a gallium nitride based compoundsemiconductor, the number of bonds of gallium (Ga), which are to bebonded to nitrogen (N), on the S-plane is two or three. The number ofbands of Ga to N on the S-plane is smaller than the number of bonds ofGa to N on the C⁻-plane but is larger than the number of bonds of Ga toN on any other crystal plane. Here, since the C⁻-plane cannot beactually formed on the C⁺-plane, the number of bonds of Ga to N on theS-plane becomes the largest. For example, in the case of growing awurtzite type nitride on a sapphire substrate with the C⁺-plane taken asthe principal plane, a surface of the nitride generally becomes theC⁺-plane. However, the S-plane of the nitride can be stably formed bymaking use of selective growth. Nitrogen (N) is likely to be desorbed ona plane parallel to the C⁺-plane, and specifically, N is bonded to Ga byway of only one bond of Ga on the plane parallel to the C⁺-plane. On theother hand, on the S-plane tilted from the C⁺-plane, N is bonded to Gavia at least one or more bonds of Ga. As a result, a V/III ratio of thestacked structure selectively grown on the S-plane is effectivelyincreased to improve the crystallinity of the stacked structureselectively grown on the S-plane. Further, since a crystal growth layeris formed along a direction different from the orientation of theprincipal plane of a substrate, dislocations propagated upwardly fromthe substrate are deflected. As a result, it is possible to reduce theoccurrence of crystal defects.

Where the longitudinal direction of the stripe-shaped opening portion ofthe mask for selective growth is taken as the (11-20) direction or the(1-100) direction, it is possible to easily form a semiconductor layerhaving a ridge line extending in the longitudinal direction of theopening portion. The stripe-shaped opening portion extending with itslongitudinal direction tilted from the (11-20) direction or the (1-100)direction by an angle ranging from about 0.2° to about 20° can be usedfor selective growth. Where the longitudinal direction of the openingportion is tilted from the (11-20) direction or the (1-100) direction bya specific angle, crystal steps tend to be made regular in the whole ofa crystal plane, so that it is possible to significantly reduce avariation between one and another of devices by forming an electrode inthe region in which regular crystal steps are formed. When using anopening portion extending in the direction tilted from the (11-20)direction or the (1-100) direction by an angle of less than about 0.2°,crystallinity of the semiconductor layer formed by selective growth fromsuch an opening portion is substantially the same as that of thesemiconductor layer formed by selective growth from an opening portionextending in the (11-20) direction or the (1-100) direction. On theother hand, when using the opening extending in a direction tilted fromthe (11-20) direction or the (1-100) direction by an angle larger thanabout 20°, other crystal steps may appear on the crystal plane.

A first conductive type cladding layer, an active layer, and a secondconductive type cladding layer are stacked on the above semiconductorlayer such as to be located on tilt planes formed on both sides of theridge line. Upon observing a facet structure of a nitride semiconductorlayer, which is formed by selective growth, using cathode luminescencein an experiment performed by the present inventors, it was revealedthat the S-plane as a tilt plane of the facet structure has desirablecrystallinity and exhibits a higher luminous efficiency when comparedwith the C⁺-plane. In particular, a growth temperature for growing anInGaN layer ranges from of 700 to 800° C. At this temperature, thedecomposition efficiency of ammonia is low. Thus, a large amount of an Nsource is required. As a result of observing the surface of the tiltplane (S-plane) by AFM, it was found that the tilt plane has regularcrystal steps and is suitable for incorporation of InGaN. In general,the state of a growth surface of a Mg-doped layer at the AFM level ispoor. However, the observation by AFM showed that the growth of theS-plane allows the Mg-doped layer to be grown in a desirable surfacestate and makes a doping condition for the Mg-doped layer very differentfrom a doping condition for the Mg-doped layer on the C⁺-plane. Whenusing microscopic photoluminescence mapping it was revealed that thesurface of the Mg-doped layer formed on the C⁺-plane by the usual mannerhas an unevenness of a pitch of about 1 m. However, when examining thesurface of the Mg-doped layer formed on the S-plane obtained byselective growth, it was found to be even and measured at a resolutionof about 0.5 m to about 1 m. Further, as a result of observation by SEM,it was revealed that the flatness of the tilt plane (i.e., the S-plane)is superior to that of the C⁺-plane.

With respect to the first conductive type cladding layer, the activelayer, and the second conductive type cladding layer, which are stackedon the tilt plane, the conductive type of the first conductive typecladding layer is a p-type or an n-type, and the conductive type of thesecond conductive type cladding layer is the n-type or the p-type. Forexample, in the case where a crystal layer having the S-plane is madefrom a silicon-doped gallium nitride based compound semiconductor, then-type cladding layer may be composed of the same silicon-doped galliumnitride based compound semiconductor, an InGaN layer may be formed as anactive layer thereon, and a magnesium-doped gallium nitride basedcompound semiconductor layer may be formed as a p-type cladding layerthereon. Thus, a double hetero structure is formed. The active layer mayhave a structure in which an InGaN layer is held between AlGaN layers oran AlGaN layer is provided on one side of the InGan layer. The activelayer may be a single bulk active layer. However, it may be of a quantumwell structure such as a single quantum well (SQW) structure, a doublequantum well (DQW) structure, or a multi-quantum well (MQW) structure.When adopting the quantum well structure, one or more barrier layers areused for separating quantum wells from each other. The use of the InGaNlayer as the active layer is advantageous in facilitating thefabricating process and enhancing a light emission characteristic of thedevice. Another advantage of the use of the InGaN layer is that theInGaN layer can be easily crystallized on the S-plane, which has thestructure from which nitrogen atoms are less desorbed, to improve thecrystallinity, thereby enhancing the luminous efficiency. In addition,even in a state that a nitride semiconductor is not doped with animpurity, the conductive type of the nitride semiconductor becomes then-type because of nitrogen holes generated in crystal. However, ingeneral, an n-type nitride semiconductor having a desirable carrierconcentration is obtained by doping a doner impurity such as Si, Ge, orSe in crystal. On the other hand, a p-type nitride semiconductor isobtained by doping an acceptor impurity such as Mg, Zn, C, Be, Ca, or Bain crystal. In this case, to obtain a p-type nitride semiconductorhaving a high carrier concentration, the nitride semiconductor havingbeen doped with an acceptor impurity may be annealed in an inert gasatmosphere such as nitrogen or argon at a temperature or 400° C. ormore, or activated by irradiation of electron beams, microwaves, orlight.

The first conductive type cladding layer, the active layer, and thesecond conductive type cladding layer extend within planes parallel totilt planes. The formation of these layers within the planes parallel tothe tilt planes can be easily performed by continuing crystal growth onthe tilt planes after formation of the tilt planes. The first conductivetype cladding layer can be made from the same material having the sameconductive type as that for a crystal layer having the S-planes. Afterthe crystal layer having the S-planes is formed, the first conductivetype cladding layer may be formed by depositing the same material whilecontinuously adjusting a concentration. Alternatively, the firstconductive type cladding layer may be configured as part of the crystallayer having the S-planes.

Electrodes are directly or indirectly connected to the first and secondconductive type cladding layers with an active layer put therebetween.Each type of electrode is formed for each device. However, one of ap-type electrode and an n-type electrode is made common to a number ofdevices. To reduce a contact resistance, a specific contact layer may beformed and then an electrode be formed on the contact layer. In general,each electrode is obtained by forming a multi-layer metal film byvapor-deposition, and finely patterning the multi-layer metal film foreach device by lithography and lift-off. Each electrode can be formed onone side of a selective crystal growth layer or a substrate.Alternatively, electrodes may be formed on both sides of a selectivecrystal growth layer or a substrate to be wired at a higher density.Electrodes independently driven can be formed by a finely processedpattern of the same material. Electrodes for respective regions may bemade from different electrode materials.

In particular, according to an embodiment of the present invention, anelectrode can be selectively formed in only a region having a desirablecrystal structure. For example, if a crystal plane has a region in whichirregular crystal steps are formed, an electrode can be formed in aregion excluding such a region having the irregular crystal steps. Thepresence of a region having irregular crystal step can be confirmed byobservation using AFM or on the basis of experience. As one example, anelectrode can be formed in a region excluding a portion on a ridge lineor a region near each end portion.

According to an embodiment of the semiconductor light emitting device ofthe present invention, a luminous efficiency can be enhanced by makinguse of desirable crystallinity of tilt planes formed on both sides of aridge line of a semiconductor layer formed by selective growth. Inparticular, in the case of injecting a current only in an S-plane,having good crystallinity, of a group III nitride based semiconductorlayer, since the S-plane is excellent in incorporation of In andcrystallinity is excellent, it is possible to enhance the luminousefficiency. In particular, to fabricate a multi-color light emittingdevice by using an InGaN layer, indium (In) is required to besufficiently incorporated as crystal. From this viewpoint, the luminousefficiency of the device can be enhanced by making use of goodincorporation of In and good crystallinity of the S-plane and thestructure is desirable for emission of light of multi-colors. In thecase of crystal growth on the C⁺-plane, gallium has only one bond tonitrogen liable to be desorbed. As a result, when crystal growth isperformed by using ammonia whose decomposition efficiency is low, it isimpossible to increase an effective V/III ratio, thereby failing toobtain good crystal growth. Meanwhile, in the case of crystal growth onthe S-plane, since the number of bonds of gallium to nitrogen on theS-plane is as large as two or three, the desorption of nitrogen becomessmall and thereby the effective V/III ratio becomes high. In general,the quality of crystal grown on not only the S-plane but also on anyother plane than the C⁺-plane becomes high because the number of bondsof gallium to nitrogen tends to be increased for growth on any othercrystal growth than the C⁺-plane. The growth of crystal on the S-planeis also advantageous in that the amount of In incorporated in thecrystal grown on the S-plane becomes high. The increased amount of Inincorporated in crystal grown on the S-plane is effective forfabricating a multi-color light emitting device because a band gapenergy is determined on the base of the amount of In incorporated in thecrystal.

In one embodiment of the semiconductor light emitting device of thepresent invention, device structure is provided, the periphery of whichhas tilt planes formed by selective growth. One conductive layer isformed in self-alignment on planes formed on the tilt planes. That is tosay, since the periphery of the device has the tilt planes, theconductive layer is formed into a shape tilted from a substrateprincipal plane. In this case, an end portion of the conductive layer isterminated at a mask used for selective growth. As a result, conductivelayers for individual devices are formed in such a manner as to bealigned only to tilt planes of each device. For example, in a devicestructure having a first conductive type cladding layer, an activelayer, and a second conductive type cladding layer stacked in this orderfrom a base body side, the second conductive type cladding layer formsthe above-described conductive layer formed in self-alignment. As aresult, the conductive layers are not required to be separated from eachother by etching. Thus, the devices can be arranged at a high density.

The semiconductor light emitting device according to an embodiment ofthe present invention is typically exemplified by a light emitting diodebut may be configured as a semiconductor laser device by formingresonators. As is well known, resonators can be formed by cleavage ofcrystal. In one embodiment, resonance planes can be formed on planessubstantially perpendicular to the longitudinal direction of astripe-shaped opening by cleavage or the like.

A display unit can be fabricated by arranging a number of thesemiconductor light emitting devices according to an embodiment of thepresent invention. In such a display, it is possible to arrange thelight emitting devices at a high density, and to facilitate thefabrication process by making an electrode common to the number of lightemitting devices. Further, the display unit can be configured not onlyas a display unit for emission of light of a single color but also as adisplay unit for emission of light of multi-colors.

First Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 1A and 1B and FIG. 2.

FIGS. 1A and 1B are a plan view and a sectional view showing a state ofa semiconductor light emitting device before and after selective growth,respectively, wherein the left side of a cutaway line shows a state ofan opening portion before selective growth and the right side of thecutaway line shows a state of the opening portion after selectivegrowth.

As shown on the left side of the cutaway line of each of FIGS. 1A and1B, in the state before selective growth, a base body 11 formed bystacking a lower growth layer on a sapphire substrate is prepared, and aselection mask 12 made from silicon oxide is formed on the base body 11.The base body 11 is formed by stacking, for example, an undoped GaNlayer and a silicon-doped GaN layer on a sapphire substrate with theC-plane of sapphire taken as a principal plane thereof. A stripe-shapedopening portion 13 is formed in the selection mask 12 by forming aresist mask on the selection mask 12 and selectively etching theselection mask 12 via the resist mask by a hydrofluoric acid basedetchant. In this embodiment, the longitudinal direction, that is, thedirection along long-sides of the opening portion 13 is taken as adirection “q” in FIG. 1A. The direction “q” is taken as a (1-100)direction or a (11-20) direction for crystal growth of semiconductorlayers having a ridge line 17.

After the elongated stripe-shaped opening portion 13 is formed, as shownon the right side of the cutaway line of each of FIGS. 1A and 1B, asilicon-doped GaN layer 14 is formed by selective growth from theopening portion 13, an InGaN layer 15 functioning as an active layer isformed on the silicon-doped GaN layer 14, and a magnesium-doped GaNlayer 16 functioning as a second conductive type cladding layer isformed on the InGaN layer 15. The silicon-doped GaN layer 14 is asemiconductor layer, part of which functions as a first conductive typecladding layer. At the time of selective growth, the silicon-doped GaNlayer 14 is grown in such a manner that the ridge line 17 thereofextends in the longitudinal direction of the opening portion 13 (i.e.,in the direction “q” in FIG. 1A). A tilt plane 18 is formed on each ofboth sides of the ridge line 17. The tilt plane 18 is a (1-101) plane(called an S-plane) or (11-22) plane stably formed at the time ofselective growth. At each of end portions on the short-sides of theopening portion 13, crystal is grown into the shape of a half of ahexagonal pyramid structure.

FIG. 2 shows a result of observing one of the tilt planes 18 formed onboth the sides of the ridge line 17 by AFM (Atomic Force Microscope).The tilt plane 18 observed by AFM has a region 18 a in which large-sizedregular crystal steps are formed. The tilt plane 18 also has smallregions 18 b and 18 c on the side relatively close to one end. Since anarea occupied by the region 18 a having the regular crystal steps islarge, an electrode can be formed substantially only in the region 18 a.Accordingly, at the time of injecting a current via the electrode,carriers seldom pass through the small regions 18 b and 18 c. Accordingto this embodiment, as compared with semiconductor layers having ahexagonal pyramid structure formed by crystal growth from an openingportion, it is possible to effectively inject a current in the planeswhich have the sufficiently regular crystal steps and thereby exhibitstable characteristics.

The tilt plane 18 mainly is the tilt plane of the silicon-doped GaNlayer 14. However, since crystallinity of the crystal plane of thesilicon-doped GaN layer 14 is directly reflected on the InGaN layer 15and the magnesium-doped GaN layer 16 formed thereon, the tilt plane 18can be substantially regarded as a crystal plane of each of the InGaNlayer 15 and the magnesium-doped GaN layer 16. In the subsequent step,an electrode is formed on a device having the tilt planes 18 formed onboth the sides of the ridge line 17, to obtain a light emitting diode.

Second Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 3A and 3B and FIG. 4. FIGS. 3A and3B are a plan view and a sectional view showing a state of asemiconductor light emitting device before and after selective growth,respectively, wherein the left side of a cutaway line shows a state ofan opening portion before selective growth and the right side of thecutaway line shows a state of the opening portion after selectivegrowth.

As shown on the left side of the cutaway line of each of FIGS. 3A and3B, in the state before selective growth, a base body 21 formed bystacking a lower growth layer on a sapphire substrate is prepared, and aselection mask 22 made from silicon oxide is formed on the base body 21.The base body 21 is formed by stacking, for example, an undoped GaNlayer and a silicon-doped GaN layer on a sapphire substrate with theC-plane of sapphire taken as a principal plane thereof. A stripe-shapedopening portion 23 is formed in the selection mask 22 by forming aresist mask on the selection mask 22 and selectively etching theselection mask 22 via the resist mask by a hydrofluoric acid basedetchant. In this embodiment, the longitudinal direction, that is, thedirection along long-sides of the opening portion 23 is taken as adirection “t” in FIG. 3A. The direction “t” is taken as a directiontilted from the (1-100) direction or the (11-20) direction by an angleranging from about 0.2° to about 20° for crystal growth of semiconductorlayers having a ridge line 27.

After the elongated stripe shaped opening portion 23 is formed, like thefirst embodiment, as shown on the right side of the cutaway line of eachof FIGS. 3A and 3B, a silicon-doped GaN layer 24 is formed by selectivegrowth from the opening portion 23, an InGaN layer 25 functioning as anactive layer is formed on the silicon-doped GaN layer 24, and amagnesium-doped GaN layer 26 functioning as a second conductive typecladding layer is formed on the InGaN layer 25. The silicon-doped GaNlayer 24 is a semiconductor layer, part of which functions as a firstconductive type cladding layer. At the time of selective growth, thesilicon-doped GaN layer 24 is grown such that the ridge line 27 thereofextends in the longitudinal direction of the opening portion 23, thatis, in the direction “t” in FIG. 3A. Specifically, the ridge line 27extends in the direction tilted from the (1-100) direction or the(11-20) direction by an angle ranging from about 0.2° to about 20°. Inthe example shown in the figures, the ridge line 27 extends in thedirection tilted from the (11-20) direction by about 5°. A tilt plane 28is formed on each of both sides of the ridge line 27. The tilt plane 28is the (1-101) plane (S-plane) or the (11-22) plane stably formed at thetime of selective growth. At each of the end portions on the short-sidesof the opening portion 23, crystal is grown into the shape of a half ofa hexagonal pyramid structure which has a short ridge line 29 obliquelyoffset from the direction “t”.

FIG. 4 shows a result of observing one of the tilt planes 28 formed onboth the sides of the ridge line 27 by AFM (Atomic Force Microscope).The tilt plane 28 observed by AFM has a region 28 a in which large-sizedregular crystal steps are formed. The tilt plane 28 also has a smallregion 28 b having a different state of crystal steps from the region 28a. The small region 28 b is located on the side relatively close to oneend. According to this embodiment, since the region 28 b is smaller thaneach of the small regions 18 b and 18 c in the first embodiment, it ispossible to more effectively inject a current in the tilt planes whichhave the regular crystal steps and thereby exhibit stablecharacteristics.

The tilt plane 28 mainly is the tilt plane of the silicon-doped GaNlayer 24. However, since crystallinity of the crystal plane of thesilicon-doped GaN layer 24 is directly reflected on the InGaN layer 25and the magnesium-doped GaN layer 26 formed thereon, the tilt plane 28can be substantially regarded as a crystal plane of each of the InGaNlayer 25 and the magnesium-doped GaN layer 26. In the subsequent step,an electrode is formed on a device having the tilt planes 28 formed onboth the sides of the ridge line 27, to obtain a light emitting diode.

Third Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 5A and 5B and FIG. 6. FIGS. 5A and5B are a plan view and a sectional view showing a light emitting diodeformed by selective growth, respectively. FIG. 6 is a side view of aportion of the light emitting diode shown in FIGS. 5A and 5B, showingone of tilt planes of semiconductor layers and an electrode formedthereon.

As shown in FIGS. 5A and 5B, a base body 31 formed by stacking a lowergrowth layer on a sapphire substrate is prepared, and a selection mask32 made from silicon oxide is formed on the base body 31. The base body31 is formed by stacking, for example, an undoped GaN layer and asilicon-doped GaN layer on a sapphire substrate with the C-plane ofsapphire taken as a principal plane thereof. A stripe-shaped openingportion 33 extending with its longitudinal direction taken as adirection “q” in FIG. 5A is formed in the selection mask 32. Thedirection “q” is taken as the (1-100) direction or the (11-20) directionfor crystal growth of semiconductor layers having a ridge line 41.

A silicon-doped GaN layer 34 as a semiconductor layer, part of whichfunctions as a first conductive type cladding layer, is formed byselective growth from the elongated stripe-shaped opening portion 33, anInGaN layer 35 functioning as an active layer is formed on thesilicon-doped GaN layer 34, and a magnesium-doped GaN layer 36functioning as a second conductive type cladding layer is formed on theInGaN layer 35. The silicon-doped GaN layer 34 is formed by selectivegrowth such that the ridge line 41 extends in the direction “q” in FIG.5A. A tilt plane 40 is formed on each of both sides of the ridge line41. The tilt plane 40 is the (1-101) plane (S-plane) or (11-22) planestably formed at the time of selective growth.

A p-type electrode 37 is formed on the magnesium-doped GaN layer 36 asthe second conductive type cladding layer. The p-type electrode 37 istypically an electrode layer having a stacked structure of Ni/Pt/Au,Ni(Pd)/Pt/Au, or the like. Each of the tilt planes 40 has a region 40 ahaving regular crystal steps. According to this embodiment, the p-typeelectrode 37 is formed into a pattern having an approximatelyrectangular shape which mainly covers the regions 40 a having theregular crystal steps. The tilt plane 40 also has small regions 40 b and40 c, each having irregular crystal steps, on the side relatively closeto one end. At each of end portions on the short-sides of the openingportion 33, a half of a hexagonal pyramid structure having a ridge line42 is formed. As shown in FIG. 6, portions of the small regions 40 b and40 c having the irregular crystal steps and the ridge lines 42 are notcovered with the p-type electrode 37. Since an area occupied by theregions 40 a having the regular crystal steps is large, the p-typeelectrode 37 can be formed substantially only in the regions 40 a havingthe regular crystal steps. Accordingly, at the time of injecting acurrent via the p-type electrode 37, carriers seldom pass through thesmall regions 40 b and 40 c having the irregular crystal steps. As aresult, it is possible to effectively inject a current in planes whichhave the regular crystal steps and thereby exhibit stablecharacteristics.

As described above, since the p-type electrode 37 is formedsubstantially only in the regions having the regular crystal steps, acurrent can be injected substantially only in the regions which have theregular crystal steps and thereby exhibit stable characteristics. As aresult, it is possible to obtain a structure in which a light emissioncharacteristic is independent of a variation between one and another ofthe devices. Since the p-type electrode 37 is not formed at steeppyramid shaped end portions of the magnesium-doped GaN layer 36, it ispossible to facilitate patterning of the p-type electrode 37 byphotolithography. In addition, the position of the p-type electrode 37can be set on the basis of a result of AFM observation, and the p-typeelectrode 37 can be formed in an area excluding irregular crystal stepson the basis of experience or the like.

An n-type electrode 39 is formed in a rectangular opening portion 38formed in the selection mask 32. The n-type electrode 39 typically hasan electrode structure of Ti/Al/Pt/Au or the like, and is electricallyconnected via the base body 31 to the silicon-doped GaN layer 34 as thefirst conductive type cladding layer.

According to the semiconductor light emitting device in this embodiment,the p-type electrode 37 is formed substantially only in the regions 40 ahaving the regular crystal steps located on the tilt planes 40 formed onboth the sides of the ridge line 42 extending in the (1-100) directionor the (11-20) direction. As a result, a current can be injectedsubstantially only in the regions which have the regular crystal stepsand thereby exhibit stable characteristics, so that a light emissioncharacteristic can be prevented from being affected by a variationbetween one and another of the devices. Since the p-type electrode 37 isnot formed at steep pyramid shaped end portions of the magnesium-dopedGaN layer 36, it is possible to facilitate patterning of the p-typeelectrode 37 by photolithography.

Fourth Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 7A and 7B and FIG. 8. FIGS. 7A and7B are a plan view and a sectional view showing a light emitting diodeformed by selective growth, respectively. FIG. 8 is a side view of aportion of the light emitting diode shown in FIGS. 7A and 7B, showingone of tilt planes of semiconductor layers and an electrode formedthereon.

As shown in FIGS. 7A and 7B, a base body 51 formed by stacking a lowergrowth layer on a sapphire substrate is prepared, and a selection mask52 made from silicon oxide is formed on the base body 51. The base body51 is formed by stacking, for example, an undoped GaN layer and asilicon-doped GaN layer on a sapphire substrate with the C-plane ofsapphire taken as a principal plane thereof. A stripe-shaped openingportion 53 extending with its longitudinal direction taken as adirection “t” in FIG. 7A is formed in the selection mask 52. Thedirection “t” is taken as a direction tilted from the (1-100) directionor the (11-20) direction by an angle ranging from about 0.2° to about20° for crystal growth of semiconductor layers having a ridge line 61.In the example shown in the figures, the direction “t” is taken as adirection tilted from the (11-20) direction by an angle of about 5°.

A silicon-doped GaN layer 54 as a semiconductor layer, part of whichfunctions as a first conductive type cladding layer, is formed byselective growth from the elongated stripe-shaped opening portion 53, anInGaN layer 55 functioning as an active layer is formed on thesilicon-doped GaN layer 54, and a magnesium-doped GaN layer 56functioning as a second conductive type cladding layer is formed on theInGaN layer 55. The silicon-doped GaN layer 54 is formed by selectivegrowth such that the ridge line 61 extends in the direction “t” in FIG.7A. A tilt plane 60 is formed on each of both sides of the ridge line61. The tilt plane 60 is the (1-101) plane (S-plane) or (11-22) planestably formed at the time of selective growth. In particular, like thesecond embodiment, since the longitudinal direction of the openingportion 53 of the selection mask 52 is taken as a direction tilted fromthe (1-100) direction or the (11-20) direction, regions in whichirregular crystal steps are formed become smaller.

A p-type electrode 57 is formed on the magnesium-doped GaN layer 56 asthe second conductive type cladding layer. The p-type electrode 57 istypically an electrode layer having a stacked structure of Ni/Pt/Au orNi(Pd)/Pt/Au. Each of the tilt planes 60 has a region 60 a in whichregular crystal steps are formed. According to this embodiment, thep-type electrode 57 is formed into a pattern having an approximatelyrectangular shape which mainly covers the regions 60 a having theregular crystal steps. The tilt plane 60 also has the small regionhaving irregular crystal steps on the side relatively close to one end.At each of end portions on the short-sides of the opening portion 53, ahalf of a hexagonal pyramid structure having a ridge line 62 is formed.As shown in FIG. 8, portions of the small regions having the irregularcrystal steps and the ridge lines 62 are not covered with the p-typeelectrode 57. Since an area occupied by the regions having the irregularcrystal steps is significantly small, the p-type electrode 57 can beformed substantially only in the regions 60 a having the regular crystalsteps. Accordingly, at the time of injecting a current via the p-typeelectrode 57, carriers mainly pass through the regions 60 a having theregular crystal steps. As a result, it is possible to stabilize devicecharacteristics such as a light emission characteristic.

As described above, since the p-type electrode 57 is formedsubstantially only in the regions having the regular crystal steps, acurrent can be injected substantially only in the regions which have theregular crystal steps and thereby exhibit stable characteristics. As aresult, it is possible to obtain a structure in which a light emissioncharacteristic is independent of a variation between one and another ofthe devices. Since the p-type electrode 57 is not formed at steeppyramid shaped end portions of the magnesium-doped GaN layer 56, it ispossible to facilitate patterning of the p-type electrode 57 byphotolithography. In addition, the position of the p-type electrode 57can be set on the basis of a result of AFM observation, and the p-typeelectrode 57 can be formed in an area excluding irregular crystal stepson the basis of experience or the like.

An n-type electrode 59 is formed in a rectangular opening portion 58formed in the selection mask 52. The n-type electrode 59 typically hasan electrode structure of Ti/Al/Pt/Au or the like, and is electricallyconnected via the base body 51 to the silicon-doped GaN layer 54 as thefirst conductive type cladding layer.

According to the semiconductor light emitting device in this embodiment,since the longitudinal direction of the opening portion 53 of theselection mask 52 is taken as a direction tilted from the (1-100)direction or the (11-20) direction by an angle ranging from about 0.2°to about 20°, the regions having the irregular crystal steps can be madesignificantly small, and the p-type electrode 57 can be formedsubstantially only in the regions having the regular crystal steps onthe tilt planes 60 on both the sides of the ridge line 61. As a result,since a current can be injected substantially only in the regions whichhave the regular crystal steps and thereby exhibit stablecharacteristics, it is possible to obtain a structure in which a lightemission characteristic is independent of a variation between one andanother of the devices. Since the p-type electrode 57 is not formed atsteep pyramid shaped end portions of the magnesium-doped GaN layer 56,it is possible to facilitate patterning of the p-type electrode 57 byphotolithography.

Fifth Embodiment

In this embodiment, p-type electrodes 71 are formed in an area excludingportions each having irregular crystal steps. For simplicity ofdescription, this embodiment will be described with reference to onlyFIG. 9, which is a side view showing a formation pattern of the p-typeelectrode 71, and regions 70 a, 70 b and 70 c formed on each of tiltplanes 70 of GaN layers.

The p-type electrode 71 is an electrode layer having a stacked structureof Ni/Pt/Au or the like. In this embodiment, each p-type electrode 71 isformed into a pattern located in the region 70 a having regular crystalsteps while avoiding the regions 70 b and 70 c each having irregularcrystal steps. The p-type electrode 71 is smaller than that described ineach of the previous embodiments. However, according to this embodiment,since the p-type electrode 71 is formed in the area excluding theregions 70 b and 70 c having the irregular crystal steps, it is possibleto suppress a variation between one and another of the devices.

Sixth Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 10A and 10B and FIG. 11. FIGS. 10Aand 10B are a plan view and a sectional view showing a light emittingdiode formed by selective growth, respectively. FIG. 11 is a side viewof a portion of the light emitting diode shown in FIGS. 10A and 10B,showing one of tilt planes of semiconductor layers and an electrodeformed thereon.

As shown in FIGS. 10A and 10B, a base body 81 formed by stacking a lowergrowth layer on a sapphire substrate is prepared, and a selection mask82 made from silicon oxide is formed on the base body 81. The base body81 is formed by stacking, for example, an undoped GaN layer and asilicon-doped GaN layer on a sapphire substrate with the C-plane ofsapphire taken as a principal plane thereof. A stripe-shaped openingportion 83 extending with its longitudinal direction taken as adirection “q” in FIG. 10A is formed in the selection mask 82. Like thethird embodiment, the direction “q” is taken as the (1-100) direction orthe (11-20) direction for crystal growth of semiconductor layers havinga ridge line 91.

A silicon-doped GaN layer 84 as a semiconductor layer, part of whichfunctions as a first conductive type cladding layer, is formed byselective growth from such an elongated stripe-shaped opening portion83, an InGaN layer 85 functioning as an active layer is formed on thesilicon-doped GaN layer 84, and a magnesium-doped GaN layer 86functioning as a second conductive type cladding layer is formed on theInGaN layer 85. The silicon-doped GaN layer 84 is formed by selectivegrowth in such a manner that the ridge line 91 extends in the direction“q” in FIG. 10A. A tilt plane 92 is formed on each of both sides of theridge line 91. The tilt plane 92 is the (1-101) plane (S-plane) or(11-22) plane stably formed at the time of selective growth.

P-type electrodes 87 and 88 are formed on the magnesium-doped GaN layer86 as the second conductive type cladding layer. Each of the p-typeelectrodes 87 and 88 is typically an electrode layer having a stackedstructure of Ni/Pt/Au or Ni(Pd)/Pt/Au or the like. Each of the tiltplanes 92 has a region 92 a in which regular crystal steps are formed.According to this embodiment, the p-type electrode 87 is formed into apattern having an approximately rectangular shape which mainly coversone of the regions 92 a having the regular crystal steps while thep-type electrode 88 is formed into a pattern having an approximatelyrectangular shape which mainly covers the other of the regions 92 ahaving the regular crystal steps. As shown in FIG. 11, unstable crystalregions located in the vicinity of the ridge line 91 equivalent to a topportion of a triangular shape in cross-section, and portions near theridge line on both end sides are not covered with the p-type electrodes87 and 88. Since the p-type electrodes 87 and 88 are formed only in theregions 92 a having the regular crystal steps, that is, are not formedin the regions with undesirable crystallinity located near the ridgeline 91 and the portions with undesirable crystallinity located near theridge line on both the end sides, these regions and portions withundesirable crystallinity can be left out of a route through which acurrent is injected. As a result, it is possible to realize a deviceoperation with stable characteristics.

As described above, since the p-type electrodes 87 and 88 are formedonly in the regions having the regular crystal steps, it is possible toinject a current only in the regions having stable characteristics, andhence to obtain a structure in which a light emission characteristic isindependent of a variation between one and another of the devices. Sincethe p-type electrodes 87 and 88 are not formed at steep pyramid shapedend portions of the magnesium-doped GaN layer 86, it is possible tofacilitate patterning of the p-type electrodes 87 and 88 byphotolithography. In addition, the positions of the p-type electrodes 87and 88 can be set on the basis of a result of AFM observation, and thep-type electrodes 87 and 88 can be formed in an area excluding irregularcrystal steps on the basis of experience or the like.

An n-type electrode 89 is formed in a rectangular opening portion 90formed in the selection mask 82. The n-type electrode 89 typically hasan electrode structure of Ti/Al/Pt/Au or the like, and is electricallyconnected via the base body 81 to the silicon-doped GaN layer 84 as thefirst conductive type cladding layer.

According to the semiconductor light emitting device in this embodiment,the p-type electrodes 87 and 88 are formed only in the regions 92 a,which have the regular crystal steps formed on the tilt planes 92 onboth the sides of the ridge line 91 extending in the (1-100) directionor the (11-20) direction, that is, are not formed in the regions in thevicinity of the ridge line 91. Accordingly, it is possible to easilystabilize device characteristics, and hence to obtain a structure inwhich a light emission characteristic is independent of a variationbetween one and another of devices. Since the p-type electrodes 87 and88 are not formed at steep pyramid shaped end portions of themagnesium-doped GaN layer 86, it is possible to facilitate patterning ofthe p-type electrodes 87 and 88 by photolithography.

Seventh Embodiment

A semiconductor light emitting device according to this embodiment willbe described with reference to FIGS. 12A and 12B and FIG. 13. FIGS. 12Aand 12B are a plan view and a sectional view showing a light emittingdiode formed by selective growth. FIG. 13 is a side view of a portion ofthe light emitting diode shown in FIGS. 12A and 12B, showing one of tiltplanes of semiconductor layers and an electrode formed thereon.

As shown in FIGS. 12A and 12B, a base body 101 formed by stacking alower growth layer on a sapphire substrate is prepared, and a selectionmask 102 made from silicon oxide is formed on the base body 101. Thebase body 101 is formed by stacking, for example, an undoped GaN layerand a silicon-doped GaN layer on a sapphire substrate with the C-planeof sapphire taken as a principal plane thereof. A stripe-shaped openingportion 103 extending with its longitudinal direction taken as adirection “t” in FIG. 12A is formed in the selection mask 102. Thedirection “t” is taken as a direction tilted from the (1-100) directionor the (11-20) direction by an angle ranging from about 0.2° to about20° for crystal growth of semiconductor layers having a ridge line 111.In the example shown in the figures, the direction “t” is taken as adirection tilted from the (11-20) direction by about 5°.

A silicon-doped GaN layer 104 as a semiconductor layer, part of whichfunctions as a first conductive type cladding layer, is formed byselective growth from the elongated stripe-shaped opening portion 103,an InGaN layer 105 functioning as an active layer is formed on thesilicon-doped GaN layer 104, and a magnesium-doped GaN layer 106functioning as a second conductive type cladding layer is formed on theInGaN layer 105. The silicon-doped GaN layer 104 is formed by selectivegrowth such that the ridge line 111 extends in the direction “t” in FIG.12A. A tilt plane 113 is formed on each of both sides of the ridge line111. The tilt plane 113 is the (1-101) plane (S-plane) or (11-22) planestably formed at the time of selective growth. In particular, like thesecond and fourth embodiments, the longitudinal direction of the openingportion 103 of the selection mask 102 is taken as the direction tiltedby the (1-100) direction or the (11-20) direction and regions havingirregular crystal steps are small.

P-type electrodes 107 and 108 are formed on the magnesium-doped GaNlayer 106 as the second conductive type cladding layer. Each of thep-type electrodes 107 and 108 is typically an electrode layer having astacked structure of Ni/Pt/Au or Ni(Pd)/Pt/Au or the like. Each of thetilt planes 113 has a region 113 a in which regular crystal steps areformed. According to this embodiment, the p-type electrode 107 is formedinto a pattern having an approximately rectangular shape which mainlycovers one of the regions 113 a having the regular crystal steps whilethe p-type electrode 108 is formed into a pattern having anapproximately rectangular shape which mainly covers the other of theregions 113 a having the regular crystal steps. As shown in FIG. 13,unstable crystal regions located in the vicinity of the ridge line 111equivalent to a top portion of a triangular shape in cross-section, andportions near the ridge line on both end sides are not covered with thep-type electrodes 107 and 108. Since the p-type electrodes 107 and 108are formed only in the regions 113 a having the regular crystal steps,that is, are not formed in the regions with undesirable crystallinitylocated near the ridge line 111 and the portions with undesirablecrystallinity located near the ridge line on both the end sides, it ispossible to stabilize device characteristics and hence to realize adevice operation with stable characteristics.

As described above, since the p-type electrodes 107 and 108 are formedonly in the regions having the regular crystal steps, it is possible toinject a current only in the regions having stable characteristics, andhence to obtain a structure in which a light emission characteristic isindependent of a variation between one and another of the devices. Sincethe p-type electrodes 107 and 108 are not formed at steep pyramid shapedend portions of the magnesium-doped GaN layer 106, it is possible tofacilitate patterning of the p-type electrodes 107 and 108 byphotolithography. In addition, the positions of the p-type electrodes107 and 108 can be set on the basis of a result of AFM observation, andthe p-type electrodes 107 and 108 can be formed in an area excludingirregular crystal steps on the basis of experience or the like.

An n-type electrode 109 is formed in a rectangular opening portion 110formed in the selection mask 102. The n-type electrode 109 typically hasan electrode structure of Ti/Al/Pt/Au or the like, and is electricallyconnected via the base body 101 to the silicon-doped GaN layer 104 asthe first conductive type cladding layer.

According to the semiconductor light emitting device in this embodiment,since the longitudinal direction of the opening portion 103 of theselection mask 102 is taken as the direction tilted from the (1-100)direction or the (11-20) direction by an angle ranging from about 0.2°to about 20°, the regions having the irregular crystal steps can be madesignificantly small and thereby the p-type electrodes 107 and 108 can beformed only in the regions 113 a having the regular crystal stepslocated on the tilt planes 113 on both the sides of the ridge line 111.Accordingly, it is possible to inject a current only in the regionswhich have the regular crystal steps and thereby exhibit stablecharacteristics, and hence to obtain a structure in which a lightemission characteristic is independent of a variation between one andanother of the devices. Since the p-type electrodes 107 and 108 are notformed at steep pyramid shaped end portions of the magnesium-doped GaNlayer 106, it is possible to facilitate patterning of the p-typeelectrodes 107 and 108 by photolithography.

Eighth Embodiment

In this embodiment, p-type electrodes 122 are formed in an areaexcluding portions having irregular crystal steps. For simplicity ofdescription, this embodiment will be described with reference to onlyFIG. 14, which shows a formation pattern of the p-type electrode 122,and regions 121 a, 121 b and 121 c formed on each of tilt planes 121 ofGaN layers.

The p-type electrode 122 is an electrode layer having a stackedstructure of Ni/Pt/Au or the like. In this embodiment, each p-typeelectrode 122 is formed into a pattern located in the region 121 ahaving regular crystal steps. Formation of the p-type electrode 122avoids the regions 121 b and 121 c each having irregular crystal stepsand portions in the vicinity of a ridge line 123. The p-type electrode122 is smaller than that described in each of the previous embodiments.However, according to this embodiment, since the p-type electrode 122 isformed in the area excluding the regions 121 b and 121 c each having theirregular crystal steps and the portions in the vicinity of the ridgeline 123, it is possible to suppress a variation between one and anotherof the devices.

Ninth Embodiment

In this embodiment, metal electrodes are formed along a ridge lineportion of semiconductor layers of a light emitting diode which has astructure similar to that described in the eighth embodiment. Astructure of the light emitting diode in this embodiment is shown inFIG. 15.

As shown in FIG. 15, like the previous embodiments, a base body 131formed by stacking a lower growth layer on a sapphire substrate isprepared, and a selection mask 132 made from silicon oxide is formed onthe base body 131. A stripe-shaped opening portion 133 extending withits longitudinal direction taken as the (1-100) direction or (11-20)direction is formed in the selection mask 132.

A silicon-doped GaN layer 134 as a semiconductor layer, parts of whichfunctions as a first conductive type cladding layer, is formed byselective growth from the opening portion 133, an InGaN layer 135functioning as an active layer is formed on the silicon-doped GaN layer134, and a magnesium-doped GaN layer 136 functioning as a secondconductive type cladding layer is formed on the InGaN layer 135. Thesilicon-doped GaN layer 134 is formed by selective growth such that aridge line extends in the (1-100) direction or the (11-20) direction. Atilt plane is formed on each of both sides of the ridge line. The tiltplane is the (1-101) plane (S-plane) or (11-22) plane stably formed atthe time of selective growth.

P-type electrodes 137 and 138 are formed on the magnesium-doped GaNlayer 136 as the second conductive type cladding layer. Each of thep-type electrodes 137 and 138 is typically an electrode layer having astacked structure of Ni/Pt/Au or Ni(Pd)/Pt/Au or the like. Each of thetilt planes has a region in which regular crystal steps are formed.According to this embodiment, the p-type electrode 137 is formed into apattern having an approximately rectangular shape which mainly coversone of the regions having the regular crystal steps while the p-typeelectrode 138 is formed into a pattern having an approximatelyrectangular shape which mainly covers the other of the regions havingthe regular crystal steps. As shown in FIG. 15, unstable crystal regionslocated in the vicinity of the ridge line equivalent to a top portion ofa triangular shape in cross-section, and portions near the ridge line onboth end sides are not covered with the p-type electrodes 137 and 138.Since the p-type electrodes 137 and 138 are formed only in the regionshaving the regular crystal steps, that is, are not formed in the regionswith undesirable crystallinity located near the ridge line and theportions with undesirable crystallinity located near the ridge line onboth the end sides, it is possible to realize a device operation withstable characteristics. Thus, it is possible to obtain a structure inwhich a light emission characteristic is independent of a variationbetween one and another of the devices.

As a feature of this embodiment, in place of formation of the p-typeelectrodes 137 and 138 in the vicinity of the ridge line, a metalreflection film 139, typically made from silver, is formed such as tocover the entire device portion. The formation of the metal reflectionfilm 139 allows light emitted from the active layer to be reflected fromthe surface of the metal reflection film 139, thereby effectivelyenhancing luminous efficiency. An n-type electrode 140 is formed in arectangular opening portion 141 formed in the selection mask 132. Then-type electrode 140 typically has an electrode structure of Ti/Al/Pt/Auor the like, and is electrically connected via the base body 131 to thesilicon-doped GaN layer 134 as the first conductive type cladding layer.

According to the semiconductor light emitting device in this embodiment,the p-type electrodes 137 and 138 are formed in the regions located onboth the sides of the ridge line extending in the (1-100) direction orthe (11-20) direction while excluding the portions in the vicinity ofthe ridge line. Accordingly, it is possible to easily stabilize devicecharacteristics, and hence to obtain a structure in which a lightemission characteristic is independent of a variation between one andanother of the devices. Since the p-type electrodes 137 and 138 are notformed at steep pyramid shaped end portions of the magnesium-doped GaNlayer 136, it is possible to facilitate patterning of the p-typeelectrodes 137 and 138 by photolithography. Since the metal reflectionfilm 139 is formed in such a manner as to cover the entire deviceportion, it is possible to allow light emitted from the active layer tobe reflected from the surface of the metal reflection film 139, therebyincreasing the luminous efficiency.

Tenth Embodiment

A method of fabricating a semiconductor laser according to thisembodiment will be described with reference to FIG. 16A to FIG. 19.FIGS. 16A and 16B are a plan view and a sectional view showing a devicestate at the time of formation of a p-type electrode and an n-typeelectrode, respectively. FIG. 17 is a side view of a portion of thesemiconductor laser device, showing one of tilt planes of semiconductorlayers and the p-type electrode formed thereon. FIGS. 18A and 18B are aplan view and a sectional view showing a device state after cleavage,respectively. FIG. 19 is a side view of a portion of the semiconductorlaser device, showing the semiconductor layers and the p-type electrodeformed thereon after cleavage.

As shown in FIGS. 16A and 16B, a base body 151 formed by stacking alower growth layer on a sapphire substrate is prepared, and a selectionmask 152 made from silicon oxide is formed on the base body 151. Astripe-shaped opening portion 153 extending with its longitudinaldirection taken as a direction “q” in FIG. 16A is formed in theselection mask 152. A silicon-doped GaN layer 154 as a semiconductorlayer, part of which functions as a first conductive type claddinglayer, is formed by selective growth from the opening portion 153, anInGaN layer 155 functioning as an active layer is formed on thesilicon-doped GaN layer 154, and a magnesium-doped GaN layer 156functioning as a second conductive type cladding layer is formed on theInGaN layer 155. The silicon-doped GaN layer 154 is formed by selectivegrowth such that a ridge line extends in the (1-100) direction or the(11-20) direction. A tilt plane 161 is formed on each of both sides ofthe ridge line. The tilt plane 161 is the (1-101) plane (S-plane) or(11-22) plane stably formed at the time of selective growth.

A p-type electrode 157 is formed on the magnesium-doped GaN layer 156 asthe second conductive type cladding layer. The p-type electrode 157 istypically an electrode layer having a stacked structure of Ni/Pt/Au orNi(Pd)/Pt/Au or the like. An n-type electrode 158 is made from Au or thelike and is formed in an opening portion formed in the selection mask152. The n-type electrode 158 is electrically connected to via the basebody 151 to the silicon-doped GaN layer 154 as the first conductive typecladding layer. End portions of the p-type electrode 157 extending inthe direction perpendicular to the ridge line are taken as approximatelylinear portions extending in the direction perpendicular to thedirection “q” for easy cleavage.

After the p-type electrode 157 and the n-type electrode 158 are formed,as shown in FIGS. 18A and 18B and FIG. 19, the device is subjected tocleavage, to form two cleavage planes 170 extending in the directionperpendicular to the direction “q” of the structure. The pair ofcleavage planes 170 function as resonance planes, to obtain asemiconductor laser device.

Eleventh Embodiment

A display unit composed of an array of a number of semiconductor lightemitting devices, which have a structure similar to that described ineach of the previous embodiment, according to an eleventh embodiment ofthe present invention will be described with reference to FIG. 20. Asshown in FIG. 20, the display unit according to this embodiment has astructure in which a number of semiconductor layers 204 are formed on asubstrate 200 by selective growth. Each of the semiconductor layers 204has a structure described in each of the previous embodiment, in which asilicon-doped GaN layer as a semiconductor layer, part of whichfunctions as a first conductive type cladding layer, an InGaN layerfunctioning as an active layer, and a magnesium-doped GaN layerfunctioning as a second conductive type cladding layer are stacked byselective growth from a stripe-shaped opening portion extending with itslongitudinal direction taken as the (1-100) direction or the (11-20)direction. A p-type electrode 205 having a stacked structure of, forexample, Ni/Pt/Au or Ni(Pd)/Pt/Au or the like, which is common to anumber of the semiconductor layers 204, is formed into a strip-shapedpattern extending in the horizontal direction, and an n-type electrode202 is formed in an opening portion 201 formed on a selection mask onthe substrate 200.

This display unit is used such that an image is displayed by lightemission from each of the semiconductor layers 204. The display unit canbe also used as an illumination unit. The number of semiconductor layers204 may be independently driven, and may be used for emission of lightof a single color or multi-colors.

According to the display unit having the above-described structure inthis embodiment, since the semiconductor layers are grown by selectivegrowth from the opening portion extending in the (1-100) direction orthe (11-20) direction, it is possible to easily stabilize devicecharacteristics, and hence to obtain a structure in which a lightemission characteristic is independent from a variation between one andanother of the devices. Also, since each of the p-type electrode 205 andthe n-type electrode 202 can be made common to the number ofsemiconductor layers, it is possible to facilitate patterning of theelectrode by lithography, and hence to simplify the steps of fabricatingthe display unit.

As described above, according to an embodiment of the semiconductorlight emitting device of the present invention, the longitudinaldirection of the opening portion of the selection mask is taken as the(1-100) direction or (1′-20) direction or a direction tilted from the(1-100) direction or (11-20) direction by an angle ranging from about0.2° to about 20°, regions in each of which irregular crystal steps areformed can be made significantly small, and a p-type electrode can beformed substantially only in regions, each having regular crystal steps,located on tilt planes. As a result, a current can be injectedsubstantially only in the regions which have the regular crystal stepsand therefore exhibit stable characteristics. Thus, it is possible toobtain a structure in which a light emission characteristic isindependent of a variation between one and another of the devices, andhence to provide a semiconductor light emitting device that is excellentfor repeatability of fabrication. Since a p-type electrode is not formedat steep end portions of crystal growth, it is possible to facilitatepatterning of the p-type electrode by lithography.

According to an embodiment of the semiconductor light emitting device ofthe present invention, an electrode can be formed in a region excludingportions with undesirable crystallinity, and a semiconductor laserdevice can be suitably fabricated by using the (1-100) direction or the(11-20) direction for cleavage.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is therefore intendedthat such changes and modifications be covered by the appended claims.

1. A semiconductor light emitting device comprising: a base body; aselection mask formed on the base body, the selection mask defining astripe-shaped opening having long-sides; a semiconductor layer formed byselective growth from the opening such as to have a ridge linesubstantially parallel to the long-sides of the opening, wherein thesemiconductor layer is a wurtzite type compound semiconductor layer, andeach of a pair of crystal planes located on both the sides of the ridgeline is one of a (1-101) plane and a (11-22) plane; and a firstconductive type cladding layer, an active layer, and a second conductivetype cladding layer formed on the semiconductor layer, wherein thesecond conductive type cladding layer is formed on the pair of crystalplanes, and an electrode is formed in a region of the second conductivetype cladding layer that excludes a portion near the ridge line and thatis located on the pair of crystal planes and which has regular crystalsteps.